Advice.....re FWB relationship?

i've been seeing this guy for a bit over a year. we met on-line and after a month of emailing, IMing and chatting, we decided to meet. during our initial meeting, we had a lot of chemistry and it became physical right away. we started seeing each other once a week for a few months, typical FB situation. however, that 1x week visit, somehow turned into 3-4x a week, overnight trips, weekend getaways, sleepovers, etc. i even had keys to his apartment. we called each other in between, texted a whole bunch and i was having a lot of fun...however, i got attached. how could i not, doing all of the things above? sharing a man's bed night after night, is intense. he would lay on me and we cuddle and we talk, really talk. and yes, the sex we had was amazing. so i started saying i love you, but he never said it back. i told myself that way ok. no strings, no commitment, that's what i signed up for, right? he also was seeing other girls for hookups in between...never knew particulars but knew. he liked 'having more' with me...he was a nice guy. hardworking, funloving, sweet, only one problem with him...he did not want a commitment. so after a year together, in april 11 i told him i was out. he respected my decision and we broke it off...now we've starting talking again and will possibly get together next week. during our 2-month hiatus he met another woman and now he's been spending weekends with her! why am i allowing myself back in his web? why do i WANT to be back with him? i know i love him...can't stop thinking about him, etc. i probably sound like im 17 yo and immature...but i'm 40 yo and very smart and should know better. advice? especially from guys would be great.