Adultery and dispute over a child

Hi there

My daughter separated last year from her husband who left her and their two week old baby in Langley with us (her parents) and he went home to Quesnel. He then had a girlfriend for about 2 1/2 months then when their baby was 6 months old, her husband only saw the baby a handful of times, but they decided to try to make things work under the understanding the other woman is out of the picture. In June of this year she caught him texting this woman again and again upon his begging she forgave him, now on Jan 1 she found out he has been talking to her all along, upon confronting the gf she confirmed they have been talking and he does not live my daughter. They were in the process of purchasing a house in Quesnel and of course my daughter is cancelling this tomorrow. His reasoning for buying a house is that if something happened he'd have a house to live in. My daughter is packing up to come home with my husband and I to Langley as there is no help or family for my daughter in Quesnel. They have a daughter she is now 18 months old and very attached to her Mom as dad has never really shown very much attention to her. We have helped raise this child for the first 6 months and are willing to help out again as her hubby has no living relatives. Would this be classified as adultery? Or what is the classification of adultery, there was never a legal seperation drawn up the first time as he was refusing to pay anything for the baby. He has threatened to sue for custody as he makes more money, she quit her job in Langley to go to Quesnel as that is where worked. She will be working when she comes back to Langley. Please advise us if what we should do or a name of a good family lawyer please. We are desperate to help her. She has no problem sharing custody but he has more money and pull.
Thank you