Is illicit online communication with a married woman—without direct meeting or incitement against her husband, and with self-restraint—considered zina (adultery/fornication)? And what is the ruling on involuntary emotional attachment to her?

Familiarity between a man and a foreign woman, whether online or otherwise, is impermissible. It is a gateway to evil and an entry point for Satan. The one who engages in it incurs sin, and the sin is greater if the woman is married due to the transgression against her husband.

If your heart becomes attached to her, you are the cause of that and will be held accountable for it, as Allah Almighty says: "And there is no blame upon you for that in which you have erred, but [there is blame for] what your hearts intended."

What occurred, such as forbidden gazes and the like, are means to zina (unlawful sexual intercourse), and may be figuratively, though not literally, called zina.

It is obligatory upon you to make sincere repentance and to frequently supplicate for this woman's husband.