Question about bfriend?

lately my boyfriend has become very boring!!! he never comes to my friends invitations or even people i know, and this is causing me sooo much frustration about don't ask it happens once in a while(he blames this to being tired all the time and a illness he has thas gives him stomach aches and headaches...we had been to the dr. a lot of time but the dr. doesnt give him answers... we have been together 4 years and he get worse and worse(i know im supposed to be there for him, but lately this patience its going right to the trash... i feel alone and not wanted...by him to tell you that i went to a party and met this guy nothing happened didn't even get his phone number and i had been infatuated for a couple weeks thinking about him and looking at the pic i took with him... its horrible.. i should not feel like this specially if i have a boyfriend... i know deep inside i care of my boyfriend but im so disappointed how boring has he became.. please help me with some advise?