Answers: People invest together all of the time.
Just brand sure you have a clear contract and an agreed, within writing, way out of the contract when/if one deputation wants out.
Are they romantically involved? It's risky any way? Are these two single relations going to stay single for the next 30 years of the mortgage? Are they going to preserve liking respectively other? Neither is going to move for work?
Getting a home with someone you are not married to is other very risky. You would be better past its sell-by date having 1 personality buy the house, then the other can rent a portion of it. Then if something happen the renter can just move lacking having to force the mart or refinancing of the house.
It happens adjectives the time. Even though people are of the divergent sex, it doesn't mean the risk is any greater. All the bank requirements to see is your creditworthiness. Have at it.