Thanks for asking about this - it happens more often than a lot of people realize.

One of the things that can affect libido is also autonomic nervous system dysfunction -- when your system is constantly stuck in "fight or flight" mode. Slow breathing exercises as well as some forms of meditation can help balance that out. There could also be endocrine/hormonal issues as a result of the TBIs

Also 16 months is not very long, in terms of TBI recovery. I recommend that you don't base your future together only on this factor -- follow up with a number of things and keep at it, and also have patience. It's good if your relationship has more to keep it together than sex.