+1
Don't touch the 401K

The first concern I'd have about this is the fact that two unmarried people are going to try to buy a house together. You'd better make sure your bases are covered if things in the relationship were to go sour. Is the mortgage and house going to be in both of your names? If one of you decided to bail and not pay the other will be screwed (along with your credit). I've even heard of one person putting their name on the mortgage and the other on the house. Then the person with the house bails and the others left with the mortgage. Just be careful. Make sure all the legal stuff is covered.