Can stress lead to decreased affection?

Yes, definitely. I think something women sometimes fail to recognize is that a man's self-worth is totally sewn up with work. Generally speaking, women seem to derive most of their self-esteem and self-worth from relationships, whilst men define themselves by what they do, their employment, what they are able to offer to society. So nothing knocks them more than being unemployed. It's very easy for them to become depressed which could lead to a lack of sex drive and a lack of communication. I have read that men say when they feel impotent in the work place, they feel impotent in the bedroom as well.
I think the key thing is to continue to give unconditional love and perhaps even more important than that - unconditional respect. It is a sign of disrespect for a man when he loses his job, when he is being told he is not necessary. For a woman to continue to respect his professional ability, continue to trust that he has the ability to provide, particularly if you're married and have children, is just what he needs to bolster his confidence.

I do think this is normal. When you are flat and depressed, you don't feel like being affectionate. Your question does not say in what circumstance your boyfriend lost his job but I have worked with a lot of people recently who have been fired and this never goes down well. Most of us do not handle rejection well. Depending on the circumstances, if he had been working there for a long time and he thought he was doing a good job and now he has been told he is not required anymore, that is a very harsh space to find yourself in. I would encourage him to get some help, to go and speak to somebody about it even though he doesn't want to talk to you he may speak with a stranger. If you could go with him, that would be even better.

It does seem sometimes like a hopeless situation, when you can't reach out to someone you care about. Yet, when the people that we care about are under pressure they often will withdraw and try to solve the problem alone. So, that might make two of you feeling helpless and two of you feeling alone.

Also it sounds like his stress at work is leading you to feel stressed as well about your relationship. I guess you're trying to support him by being talkative and he's not responding. You're also trying to be physically affectionate. He's not responding to that at all. There may be some ways that you can support him without having to directly address the stress at work.

You may try going out somewhere or enjoying time with friends, and try to take his mind off of being in a place where his mind will be taken off work may just be a temporary solution.

Yes, stress can lead to decreased affection in relationships. Some individuals when stressed will withdraw as they try to work through the issues themselves, unemployment is often associated with feelings of worthlessness and incompetence and those feelings can make it hard for the individual to ‘face’ their partner in these circumstances. 
Often, as partners and friends we feel that we should be able to help ‘fix’ the problem but this will often make the person suffering feel less empowered. You can help your boyfriend by practicing a skill known as active listening. When he does talk to you don't try to offer advice as but just sit with him, listen to what he is saying and reflect back to him what he has expressed e.g ‘that must feel very frustrating’ if he feels he has space to talk without being judged then he will be more likely to open up.
If you are concerned about his mental health you could ask him if he'd considered talking to a professional, he may be more likely to open up to someone he doesn't know who is skilled in this area.   

Stress can definately effect a person's interest in affection. Losing a job also can have a big impact on self confidence.  Given that he is saying that the only problem is stress, I would suggest you do what you can to help him get focussed and active in job hunting.  He will regain a sense of purpose and hope once he starts making progress with securing a job.  Also, it would probably be helpful to discuss how the finances can be managed while he is not earning. 

I you think he is not making progress after a couple of weeks, he should see a GP and get a referral to a psychologist for more assistance.

Stress can definately affect the closeness of a relationship and intimacy. Your boyfriend is struggling with the emotion of losing his job which we would say is similar to a grief reaction. Support him by just being there for him and being a listener when he wishes to talk. I agree with Simon that if he is still strugggling in a couple of weeks he should talk to his GP

The stress of losing employment can be a major problem for people as they grapple with financial issues and also a sense of worth . Your boyfriend may not be as emotionally available as he would normally be as her assesses where he is at. It is great that you are open to understanding his sensitivity to the change. Encouraging him to follow all his options and reminding him of his strenghts may facilitate his sense of worth but ultimately he will have to find a way forward with this challenge .

As a guy that's going threw this in the way of a back injury lost me my job and to make it worse my ability to play with my child outside.

what you are doing is spot on and trust me we may not show much back because of how angry we are with ourself but deep down we do see what your doing for us and slowly try to show you affection back.

to me time with best mates male time is best quick fix as this is what ya do when work and can afford to hang out with mates. But it becomes hard when mates talk about work and things they buy and do and your just at home doing nothing you know.

in saying that if these mates show that they don't judge or care about his job and actually try look for work for him or shout him drinks lunch fuel anything to feel like a man again I can bet that that night or next day he will talk or smile or be affectionate with you may not last long but it works.

its this or he loses his mates one by one gets worse and you lose your friends or your friends say why do you bother that gets in your head yet when his good feels like a man working all that stuff if his your perfect guy when all was good then do not give up and do not say things like since your not working can you do house stuff or renovate for some reason that makes us more angry when ya would think doing something would help hey. 

I hope as a male view this helps him and you.