If your boyfriend is on 50 and you are on 34 , you should be able to get mortgage approval for €202k easily enough. Have you asked the lender would they allow him take over the mortgage?
1) Agree a valuation with your friend - say €190k
2) Your boyfriend buys her half of the house for €95k
3) She is freed from €101k , half the €202k mortgage, so she owes you €6k.
The bank should agree to it.
I know you and your boyfriend might be madly in love, relationships break down. Do a joint ownership agreement before he takes over his share. You have to discuss what happens if you break up and are in negative equity and what happens if you are in positive equity.
Brendan