What sort of help you do seek if you already did
mention that you don't mind being the third party? I seriously
doubt anybody gonna support your choice to be a third party, make
yourself miserable and ruin those who are involved, including
yourself, in this triangular love affair.
If your man is sincere, he would abandon his current relationship
to pursue one with you. Apparently, he chose the two timing option
because it's non-committed.
Do you consider that as love? Or is it just very convenient way of
doing things?
He isn't liable for any responsibility because the 'unwritten
clause' in this sub rosa relationship is non-commitment. You are
needed when there's a need for you to fill in his emotional chasm
created by his current relationship. At the end of the day, he goes
back to his woman WHOM he has the burden of responsibility over and
you are kept away like a discarded toy.
Is that the way of love you seek?
He employed flippant words to retain your feelings; but does that
amount to anything? Yeah, missing you... loving you... and all that
typical sweet nothings that an inexperienced woman would fluster in
love excitement - has that spur any initiative, actions or plans he
has for you since actions speak louder than words and if he does
love you, the former would materialise?
Nothing.
It seemed to me that you enjoyed his company and doesn't mind going
out with him even that tantamount to be playing with fire.
Perhaps only when the fire sear you badly, would you then deter
yourself from such foolishness that doesn't have an end to begin
with. 
Cheers
