It isn't an ideal relationship and i know that i will lose him eventually because of my lack of commitment.
No , you will lose him when his wife finds out . Have you not asked yourself why he is being so careless ?
Does it not strike you as odd that he agreed to reconcile with her although he was involved with you ?
Why on earth would he agree to reconcile with a wife he cant stand when hes in love with you ?
If it helps to see it from someone elses point of veiw here goes,
I DIDNT want a divorce , i wanted my husband to realise how important our marriage was and acknowledge that we had some problems.
In my own bizzare way i did this by having an affair.
When DH didnt pick up on my extravagant clues i TOLD HIM.!!!!
And NOT because i wanted him to leave , i was insecure and pathetic and wanted him to notice me .I will also add that some of this fell into the revenge category that lots of affairs do for slight wrongdoings over the years.
Sadly it looks like you are there to fix his fragile ago and to help him get revenge on his wife , he probably still loves his wife or else why would he still be there ?
He might well beleive the things he says to you , he might not be a horrible person ( i dont like to think i am ) but i said horrible things about my DH that werent true and i didnt mean.
Regarding him slagging his wife off , he sounds quite angry towards her which doesnt make sense if hes so caught up with you.
For your own sake , and theirs , get out of their marriage and stay out. You are deluding yourself that theres anything more to it im afraid.