very strange to think that husband cheats at this ripe age, 35 ysrs after marriage. Wud it have been matrimonial peace, no such person wanders away to somebody else. Anyhow, without touching the reasons behind, see what law says:
* R u sure that they have married. Any proof? Living 2gather is not covered under MARRIAGE
If you have prove, put 494IPC (bigamy) case, he wil be punished as per law
* If the 2nd girl is unmarried b4, is >18yrs old & living with consent with the husband, u cant do much
* At the most u may put Adultry charges upon husband, but remember:
a) Ur marriage wont survive if u put any police case or legal petition
b) Finding adultry proofs are next to impossible
c) Civil remedy for adultry lies in SEEKING DIVORCE ONLY...which u dont want
d) Criminal case of adultry wil be filed against ur husband only, not on that girl. If the couple is somewhat cautious, u can nail the husband either, this way.
* No law can prevent him from meeting this girl or living with this girl. No law forces him t live wid u.
Now what is better solution-------
1) reach the root of the problem, why is he interested in leaving the household. If possible address this real issue.
2) talk ur heart out with the husband n find way out
3) involve elders who can reach at some way out
4) secure ur own & children's financial needs & let him go where he wants. Unilateral wish to cohabit does not bear fruit.