OP - you need to get to the bottom of his problem. Could be abuse from years ago, could be that he's shy about admitting to his fetish (whatever that is), could be that he is actually gay and finds the idea difficult to confront (unlikely to be honest) - could be any number of things but you can't just go on and on with the status quo...
As a bloke I know that I could never become fully involved with a woman who I didn't want to have sex with and I wouldn't expect (or want) a woman who didn't want the same to become involved, committed to or invested in me. For me, and I think most people, sex is a fairly big part of the jigsaw. At present you are giving him his jollies via a good blow job once a week while he buys flowers. Hmmm... It's either sex both ways or no sex. A one sided sexual relationship will, wether you are explicitly aware of it or not, spill over into other areas of your relationship and you will end up being on the wrong end of it.
Get drunk together - smoke a bit of weed - whatever it takes to loosen his tongue (forgive the pun) and let the talk wander into new territory about him, his desire, turn ons, needs - and see where it goes. If he knows you're 'on his side' he will open up to you and you may discover a way to re-ignite a sexual flame in him or at least discover where the problem lies. This will take more than one attempt ! Trust in this sort of area takes a while to establish even within a long term relationship.
Try it and see if you can get somewhere. If you can't then I have to be honest and say that I would start looking for a way to bring things to a dignified end.
The notion of 'taking a lover' is spurious and only good for novels and bad TV. A "bit on the side" will go horribly wrong and if you find yourself single in weeks or months you can have as many lovers as you like guilt free and with no recriminations. But try to fix things first because it sounds like you love a decent man who has a problem which can probably be addressed.