Apart from Robert Spryngolde, Master Aleyn is Margery Kempe's special ecclesiastical friend and champion. He's also an intellectual heavy-hitter: a Cambridge-educated doctor of divinity and Carmelite friar who compiled an index for St. Bridget of Sweden's Revelations. He's perfect for Kempe.
Though he has mixed luck in defending Kempe from her detractors in Bishop's Lynn (including the "Good Friar" who publicly disses her), his friendship is valuable to her. At one point, Master Aleyn's superiors decide that his relationship with Kempe is either not beneficial for him or maybe too warm, if you get our drift, so they command him to stop seeing her. Kempe's confessor Robert Spryngolde also advises her to leave Aleyn alone, which makes her very miserable for a time.
Along with Robert Spryngolde and other minor clerics in the area, Master Aleyn works hard to keep Kempe out of trouble. He tries to negotiate with the Good Friar on her behalf, and he meets with Kempe, Master Robert, and John Kempe in West Lynn to advise her after she has been arrested several times in England.
Kempe has a revelation that assures that Master Aleyn, barred from her sight and now gravely ill, will survive until they have a chance to chat again. That revelation turns out to be true, and the scene of their reunion is one of the most joyous moments in the whole book:
There was a dinner of great joy and gladness, much more spiritual than bodily, for it was sauced and savoured with tales from holy scripture. And then he [Master Aleyn] gave the said creature a pair of knives, in token that he would stand with her in God's cause, as he had done before. (I.70.210)
Though it's difficult to tell through Kempe's voice alone, it seems that the friendship between her and Master Aleyn is both genuine and holy.