The gastrointestinal side effects you describe have only occurred in less than 5% of Humira patients in studies. In all honesty, I had never heard of vomiting and bloody stools as a Humira side effect until I researched it to form my response. Are they sure that Humira was the cause, and not another autoimmune condition like Crohn's disease, which often occurs alongside spondylitis?
I'm not aware of any research supporting his statement that Humira can effect fertility. It certainly isn't a listed side effect or in the prescribing information anywhere that I can find. If he's taking Methotrexate along with the Humira (many patients do), that could be what he was talking about. Here's some more information about what they do and do not know about the effect of Methotrexate on male fertility (circa 2003; others may chime in with more recent information presuming he is indeed on methotrexate): http://www.motherisk.org/prof/updatesDetail.jsp?content_id=663
If he is on Methotrexate, it can also cause some of the gastrointestinal symptoms he is experiencing.
Sulfasalazine is another arthritis medication that can cause male infertility. Lyrica (pregabalin) is used to treat fibromyalgia and pain, and can also cause male fertility problems.
If he is indeed having so many side effects from Humira, there are other medications in the same class to try. I'm not sure what all he has access to wherever you are (I gather you're not in the USA by your use of the term A&E), but it's unlikely he'll experience the exact same side effects from another medicine like Enbrel, Simponi, or Remicade.
Not to be too callous, but as a woman who wants to have children someday, I've also made the decision to take several medications over the last few years that may decrease my fertility. I never really consulted with my husband about the decision either, but he supported me when I told him about the fertility side effects. Given my pain and the damage my inflammation can and will do to my body, it's a decision that makes sense for me (and for us). To be quite honest, your boyfriend may not care at this point, and while that isn't terribly sensitive to your feelings (and he absolutely needs to communicate with you about it), I don't really blame him. One mildly good thing is that the problem of male infertility is in many ways "solved" more easily than that of female infertility, in that using sperm donors is typically less expensive and far less complicated than options like in vitro fertilization or surrogacy. Sure, you may prefer to have a child that is 100% genetically the product of you and your significant other, and I don't know that he feels this way, but he wouldn't be alone if he has some misgivings about potentially passing AS along to his future kids.
It does sound like he is having some communication problems. There are definitely aspects of his health that you two *need* to communicate about. You're right that the burden of someone with AS is very much also the burden of the person who shares their life with them. Maybe some sort of couples therapy is in in order? He might benefit from therapy on his own too. Depression is unfortunately very, very common with chronic diseases and chronic pain.