An idea for you, Ladyzero...

Your having sex with the bf would be a Pareto improvement. http://en.wikipedia.org/wiki/Pareto_efficiency

Would it hurt you? No, you do not report having suffered from painful sex in the past. Guilt feelings or anything like that? No, you enjoy masturbation and the like and are comfortable with your sexuality. Do rape memories and flashbacks haunt you? Nope. Is the guy abusive? No, not at all. He cares enough to send you frequent texts. And not to embark on a search for another woman. For a whole year. Which is impressive. So sure, a depressed woman may not enjoy sex positively, but she will not suffer. It will be at worst a neutral experience. And for the guy it would be a positive experience. So overall, it would be an improvement - at worst you would be no worse off and he would be better off, so as a team they would be better off. So why not go ahead?
Plus, you are depressed. Your adult children have abandoned you. YOu probably feel unloved, unappreciated, etc. Reconnecting with the guy sexually would improve the situation in this department - you would see that someone cares for you and appreciates you. That is huge!
Further, nice people usually enjoy seeing/feeling the pleasure of their partners, and you are clearly a very nice person. So the guy's orgasm and the guy's satisfaction would be positive experiences for you. Even if you yourself are not in the mood for sex.
It is known that the elderly fair better when they volunteer. Doing something nice for others feels good for humans, even if you are too depressed yourself for earth-shattering orgasms. Or, if your medications have erased the drive and rendered you anorgasmic.
I am not talking about doing something against your will or suffering, clearly, the way BigMama suffers. I am just talking about being nice and doing acts of loving kindness that would most likely make us feel good and bond us to our fellow human beings.

I will tell you a relevant story from my life.

in 2006, just diagnosed bipolar and on short term disability from work, I accidentally trapped a huge, ferocious black cat. Male. The size of a mountain lion. I did not mean to trap him. I was trying to catch a domestic escape artist. But instead I trapped that monster. Clearly feral and clearly untameable.

I contacted the head of my local cat rescue agency from whom I had earlier borrowed the trap, asking her what to do. She gave me a voucher to take to our county's Low Cost Spay and Neuter clinic to have the monster fixed and immunized. And later keep him near the house and feed him while he heals and then release. Trapping, fixing, and releasing is the most effective and humane way to control the population of feral cats and I knew it.

With the voucher I would pay only fifteen bucks for the procedure, much less than at a private vet's. But only one clinic accepted the vouchers. For several days I had to call the clinic at six in the morning, getting up earlier than I otherwise would have had to. But fine, I was off work and could sleep later in the day. Finally the clinic gave me a spot and I put the horribly heavy trap in the trunk. Oh, and during those few days of waiting the monster made such scary sounds when I put food inside the trap that I was afraid that he would bite my hand off.

That was my single good deed as far as humane control of feral cats' population goes. I returned the trap afterwards. I do know women volunteers who own their traps and regularly trap, fix, and release. This is definitely laudable, and maybe one day I will join them, but not now. Still, if, god forbids, one of my kitties runs away and I need to trap him or her but instead trap a feral, I would definitely spend fifteen dollars, a little cat food, and a couple of mornings of my time to have the feral fixed. Why would I not do a good deed that costs me so little?

You already have the cat. The boyfriend. I would not encourage you to get into a whole lot of new relationships, as I do not think that being depressed is the right time for it. So definitely not make extra effort and get out of your way, no. Just deal with the cat whom you happened to have trapped in a humane manner. What would it cost you? Just to take a shower and put on clean clothes. I know it is a lot for a depressed person but the satisfaction from treating the boyfriend in a nice, humane, caring manner would be worth the effort. I do not know why but most humans enjoy helping others and being a little altruistic. Maybe because humans are social animals and altruism is necessary for socialization. Maybe evolutionary psychology has something insightful to say about it.