Thank you everyone.
nycindie I guess I may be confusing the term FB. He certainly loves the others and has loved most of them in the past. He is actually a very loving natured person. They seem to love him too - and they SAY they think a lot of me. I find htat hard to believe... maybe I am wrong but I assume they MUST be looking down on me, thinking I am inadequate for him to be needing them. I on the other hand couldn't contemplate actually loving anyone else but him - tbh the thought scares me. I don't want the baggage of another person's emotions.
GroundedSpirit when we do have sex it's fine... no not stunningly earth-shattering, but pretty good and satisfying enough and there is variety. The biggest issue is the infrequency which is often to do with him being tired when we are together and because he's well-satisfied elsewhere it just doesn't seem to occur to him that I might be feeling in need.
rory yes the lying, treating me a bit like a parent who'll spoil his fun is a salient observation. And yes that's the only area where there is a problem. He regularly takes me to lunch, offers to shop, cook tea etc. If I am ill, he is super-attentive. I enjoy his company very much and I can't imagine wanting to be with anyone else. He tells me frequently that he loves me and would do anything for me.... In the past when things have come to a head and re-settled down, we've spent a period of time with either me knowing what's going on or with him claiming to have "given it up"... but of course it is only until next time he finds someone new.
This is why I think maybe it is me that needs to change? Apart from this one area, things are good. I need to deal with my frustration and the resultant jealousy that someone else is getting what I want! I think if there was someone I could be open with and talk to it'd help. I don't have any close friends, certainly not any who I could tell as they'd all be so shocked and the revelation would almost certainly cause major ructions in our social life, and that'd benefit nobody, least of all me.