Generally exposing the affair to family and friends is counter-productive if you still hold out hope for reconciliation. But I think it’s fine to let him know that you know he’s been having an affair. Don’t say anything about when it started - he’ll lie anyway, and you can be 100% sure it started before he dropped the bomb. (In fact, you need to see you gyn and be tested for STDs. Sorry. )
As for barring him from the house - check you legal status first. If he co-owns the house it may not be legal to change the locks. But it’s fine to establish boundaries - just don’t make it about OW, that’s giving her too much power. Try “you’ve decided not to be my husband and this is not your home any more. “
