Originally Posted by
CliffordK
I would consider a full road bike... Carbon Fiber if you wish. Every little bit helps. Definitely don't rider a cheaper bike than your partner.
Get your BF an old 80's model steel MTB
And, if going for a picnic, or running to the store, make him also drag a trailer.
As
Drew Eckhardt mentioned, a lot depends on your riding. You said you are commuting... which can rack up a lot of miles. How far? Perhaps try pushing a bit further.
Speaking from personal experience, riding 5000 miles in a year won't get you past somewhere between "slow" and "not fast."
You need intensity to get past that plateau.