Plz helpmy best friend is leaving his gf and start acting weirdly with me what can I do about that?

my best friend was a person that I always care of .. he is just my best friendi know everything abot him and he also but he has a gf and if I were honest I limit my talking with him at some point bcs of that
but so recently he had a hard time and I offered to help as always but when he skip that he start acting weirdly and he is showing an attention I didn't see it before
and he dont talk to his girlfriend he is even off line and talking just to me and wait for me all the time and if I were honest he said to his girlfriend that he will be off line for a while and in that time he speak with me and put me in pressure by doing things i've never seen it from him
but I don't like that and it hurt seeing his gf waiting and idot want this
what can I do now I talk to him or not im lost
and sorry if my english is broken