It sounds as if your OH is feeling a little insecure and not certain of where he stands in your affections, Why. Such a feeling may be completely unjustified but emotions are rarely logical.
If he's spending all his time in his workshop, perhaps it's because he's convinced himself that he doesn't much matter to you and so he's occupying himself in the best way he can?
Perhaps, rather than just bringing home another cat, which would only convince him that his views don't count, you should sit down and talk to him. Reassure him that you do love him and want to spend time with him. Come up with some plans for things you can do together - outings, weekends away, home improvements, learning a language, joining a local social/activity group or just sitting at home watching a movie together.
If he doesn't want to participate, then fine - at least you will have tried and maybe then will be the time to find another cat. However, if your life together takes an upturn then, once he feels a bit more secure and certain he's number One in your life, then he might well be more prepared to accept another cat.