Aaron, it is very nice to hear from you again!

As long as the Gerushah is still with the Kohen, he may not eat Terumah.

1. The sources for this are as follows. The Mishnah in Sotah (23a) lists several differences between a "Kohenes" (the daughter of a Kohen) and a male Kohen. One of the differences is that a Kohenes can become a Chalalah (Rashi explains that this means that she becomes disqualified from eating Terumah if she has relations with a man who is forbidden to her), while a Kohen cannot be come a Chalal (a disqualified Kohen) if he married a Gerushah. The Gemara in Sotah (23b) states that this is derived from the verse, "And he must not profain his seed..." (Vayikra 21:15), from which we learn that these activities render the Kohen's descendants Chalalim, but these activities do not make the Kohen himself a Chalal.

2. However, the Rambam, in his commentary to the Mishnah on Sotah, writes that when it states that the Kohen does not become a Chalal, this means that he will never become a permanent Chalal. He is, however, invalid as long as he remains with this woman, but if he divorces her and vows that he will never marry a prohibited woman he may return to serve in the Beis ha'Mikdash and to eat Terumah, etc. In contrast, a Kohenes is profaned for the rest of her life.

3. The Shulchan Aruch (OC 128:40) states that if a Kohen married a Gerushah, we do not treat him as holy ("Ein Nohagin Bo Kedushah"), and he may not bless the people. The Mishneh Berurah (#147) writes that he is disqualified mid'Rabanan for every aspect of Kehunah until he publicly vows that he will leave the Gerushah.

4. Accordingly, it would appear that the Kohen who married the Gerushah is forbidden only mid'Rabanan from eating Terumah. However, Rav Elyashiv zt'l, in He'oros Al Maseches Sotah (p. 137), cites the Teshuvah of Rabeinu Eliyahu Mizrachi (#59) who states that the Kohen is a Chalal mid'Oraisa as long as he does not leave the Gerushah. Rabeinu Eliyahu Mizrachi cites proof for this from the Toras Kohanim on the verse, "The Kohen may not become Tamei in his people to make him defiled" (Vayikra 21:4). The Toras Kohanim learns that "if he behaves this way, he is defiled... but if he leaves this way, he remains in his holiness." It appears from this that while the Kohen is with the Gerushah he is forbidden mid'Oraisa from eating Terumah.

Kol Tuv,

Dovid Bloom