- A Flesh Form keeps all the attributes, skills, knowledges, Awakened status, Cyberware, Bioware, etc, of the physical body. The Spirit Ally merely becomes a puppet master.
- The Spirit Ally cannot astrally project while in Flesh Form.
The Inhabitation power is explained in pages 195 and 196 of Street Grimoire, but, as with many things in SR5, it's not very clear and you have to infer many things through careful reading.
There can be three outcomes for an Inhabitation:
True Form: [...] The vessel is irrevocably destroyed or consumed during the process. [...] The true form bears no resemblance to the vessel and retains only the knowledge, skills, and attributes of the spirit alone.
Hybrid Form: [...] Both vessel and spirit become a single, dual-natured entity (p. 395, SR5). The hybrid form’s physical attributes are enhanced by the spirit’s Force. The spirit retains all of the host’s natural abilities but only some of its memories and none of its skills (the spirit retains its own skills, however). [...] Unlike Possession spirits, hybrid forms can operate a direct neural interface, and the vessel’s cyberware (if any) continues to function for the spirit.
Flesh form: [...] A perfect combination between spirit and vessel, the flesh form retains all of the vessel’s abilities, knowledge, and skills (except Conjuring skills), and its appearance is virtually indistinguishable from the original vessel.
The three outcomes follows a basic progression that can be summed as:
- Fail for the True Form: nothing coming from the body is kept, only the Spirit's stats are kept,
- Moderate Success for the Hybrid Form: some stats from the body are kept, the Spirit alters some of it and fills in the rest;
- Complete Success for the Flesh Form: everything from the body is kept, the Spirit doesn't influence the stats at all.
Thus, when Inhabitation results in Flesh Form, you basically keep the character sheet of the PC or NPC as is, only the personality changes since a new spirit is inhabiting the body.
In your example, if the summoned Ally Spirit isn't the spirit of the loved NPC; which would be highly unlikely unless you as GM allow it; the Ally Spirit will remember the love between the NPC and the PC, but is in no way forced to follow up on it. It would be a memory with no feelings associated to it, akin to watching a movie.
As for Astral Projection, the description of the Inhabitation power explicitly forbids it:
The spirit cannot be separated with Banishing, and the spirit cannot voluntarily leave the vessel. An inhabiting spirit is only disrupted when its vessel is either destroyed or killed from Physical damage overflow (p. 209, SR5).
Since Astral Projection means sending one's spirit/mind/consciousness away from the body, a Spirit inhabiting a physical body cannot astral project. They can still see in the astral plane in Flesh Form thanks to gaining the Dual-Natured powers.